Front

What is a sextant?

Back

A sextant is an instrument used to determine the angle between the horizon and a celestial body such as the sun, moon, stars, or planets, primarily for celestial navigation.

Front

What does the term 'sextant' derive from?

Back

The term 'sextant' comes from the Latin word 'sextus', meaning 'one-sixth', as its arc spans 60 degrees, or one-sixth of a circle.

Front

What is the purpose of the index arm in a sextant?

Back

The index arm pivots at one end to allow the attached index mirror to reflect an object onto the horizon glass and swings along the arc scale to indicate the angle.

Front

What is the function of the micrometer drum in a sextant?

Back

The micrometer drum rotates to make fine adjustments when measuring angles and indicates minutes of a degree of angle.

Front

What is the significance of the horizon glass in a sextant?

Back

The horizon glass allows the observer to view one object reflected next to it, with half of the glass silvered to act as a mirror.

Front

What is the process of taking a sextant reading?

Back

To take a sextant reading, point the sextant to the horizon, clamp the index bar, bring the celestial body down to the horizon, release the clamp, adjust the position, and read the angle.

Front

Define 'sensible horizon'.

Back

The sensible horizon is a small circle on the celestial sphere on a plane that passes through the observer's eye, contained between the heavenly body and the visible horizon.

Front

What is the difference between the visible horizon and the geographical horizon?

Back

The visible horizon is the intersection of the observer's line of sight with the Earth's surface, while the geographical horizon is a plane that passes through the center of the Earth and is perpendicular to the observer's vertical.

Front

What is the purpose of the Nautical Almanac?

Back

The Nautical Almanac provides navigational information to mariners, including data on celestial bodies' positions and movements, tides, and currents.

Front

What are the main components of the Nautical Almanac?

Back

The Nautical Almanac contains astronomical data necessary to determine the position of celestial bodies, including GHA (Greenwich Hour Angle) and declination.